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Could dinosaurs climb trees? How should we define "climbing"? What types of dinosaurs may have "climbed" trees? How did they climb them? What proof do we have? Did climbing lead to flying?

Many animals such as goats can get into trees yet are not considered climbers.

Likewise many dinosaurs could probably also get into trees, particularly those that were small enough and needed to, say, get away from predators in a hurry.

But it's not until an animal starts going into a tree in order to forage for food that specialisations associated with climbing emerge.

"Among dinosaurs, the group most likely to include specialist tree climbers is Deinonychosauria ('fearsome claw lizards')," says Dr Steve Salisbury, a palaeontologist from The University of Queensland.

Fossils of deinonychosaurians are known from all over the world including Australia, which during the reign of dinosaurs was part of the southern supercontinent of Gondwana.

Deinonychosaurians are maniraptoran ('seizing hands') theropods ('meat-eating') that include troodontids, and dromaoesaurids such as the well-known Velociraptor as seen in the movie series Jurassic Park, explains Salisbury.

Deinonychosaurians and birds most likely shared a common ancestor that lived in the Late Jurassic, 160-150 million years ago.

Getting into trees is one thing

"Some recently discovered deinonychosaurians from China dating back to the Early Cretaceous 130-125 million years ago show characteristics that indicate they were quite capable of getting up into and moving around in trees," says Salisbury.

"They were small, bipedal and had long curved claws on both hands and feet. A lot of them were also feathered and — barring their long bony tails and sharp teeth — looked a lot like birds today."

One example was the four-winged, canary-sized Microraptor, boasting iridescent black feathers similar to those of a satin bowerbird.

Like other near-bird maniraptoran dinosaurs, Microraptor had a fused semi-lunate (crescent-shaped) carpal bone in the wrist, explains Salisbury.

"This allowed them to swivel the wrist and fold the forearm (or wing) like modern birds. It also may have permitted a movement ideal for going into trees. By hugging the trunk, these dinosaurs may have been able to pull themselves up."

Having a long, stiff tail also probably helped, he says. "This could be used as a strut for bracing the body while moving upwards, much like a woodpecker uses its tail on a vertical tree truck while foraging."

Climbing trees is quite another

Such specialisations on their own, though, don't necessarily mean these dinosaurs could climb per se, says Salisbury. The important thing was whether they could actually hold on to vertical surfaces using their claws.

"Among living birds, the curvature and length of the claw closely correlates with climbing ability. While many birds can perch and hop around in trees, only a few can use their claws to cling to and climb up them."

In one study, anatomists at The University of Queensland found that claw curvature and length in the majority of deinonychosaurians resembled that seen in ground-foraging birds such as pigeons and cockatoos.

"The latter can perch and hop around in trees but they can't cling to or climb them. Therefore the same was probably true for their dinosaurian forebears," says Salisbury.

Up, up and away

There is another way to get up into a tree, however, that is significant in terms of the origin flight, he says.

"Recent research suggests that many ground dwelling birds including quail and partridges engage in what is referred to as 'wing-assisted incline running', explains Salisbury.

"By flapping their wings, these animals are able to produce enough forward directed thrust to enhance traction on vertical surfaces such that they can literally run up tree trunks.

"There are many examples of feathered deinonychosaurians. Yet only a few possessed the asymmetrically veined wing feathers that enable powered flight," he says.

"The majority had either quite rudimentary wings and/or wings with symmetrical or non-veined feathers. While flapping such 'wings' might not have lifted them off the ground, they may have been sufficient for wing-assisted incline running."

Once these dinosaurs could get into trees, jumping and gliding between branches became possible as wings can be used for different things, says Salisbury.

"In many respects, climbing is just a stepping stone to flying in the transition from ground-dwelling dinosaurs to birds."

Dr Steve Salisbury from The University of Queensland was interviewed by Kathy Graham.

Comments (4)

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Dann :

18 Apr 2012 12:26:14pm

"There are many examples of feathered deinonychosaurians. Yet only a few possessed the asymmetrically veined wing feathers that enable powered flight."

Asymmetrical feathers aren't necessary for powered flight. Some modern birds manage quite well with symmetrical flight feathers. Asymmetry in flight feathers may have more to do with improved wing folding than flight.

Steve Salisbury :

19 Apr 2012 10:15:45am

Thanks for your comment Dan. There are two types of feathers on the wing on a flying bird. The secondary and tertial flight feathers, which are attached to the forearm (ulna) and upper arm (humerus) respectively, have symmetrical veins. These feathers help give the wing its aerodynamic profile, and a typically held with their long axis parallel to the direction of flight. Primaries flight feathers are connected to the hand (the fused carpometacarpus and phalanges). Unlike the secondary and terial flight feathers, primaries have asymmetrical veins, and are much longer than secondary and tertial flight feathers, and can be individually rotated. During flapping flight, primary flight feathers are main way that a bird can use its wing to generate forward directed thrust, with most of this happening during the downstroke. On the upstroke, however, the primary flight feathers are separated and rotated, reducing air resistance while still helping to provide some thrust. Separated primaries may also act as individual 'winglets' to counteract stalling. A high angle of attack on the main wing when a bird is coming in to land causes it to stall, but the primaries twist in the airflow, reducing their angle of attack and continuing to provide lift and thrust. The flexibility of the primary flight feathers on the wingtips of large soaring birds, such as eagles and vultures, also allows for these feathers to be spread into ‘fingers’, which can be twisted and staggered by the airflow to make the wings more efficient at low speed, reducing the creation of wingtip vortices.

Without symmetrically veined primary feathers, a bird is not able to fly. If you want to stop your chooks from flying out of their pen, all you need to do is clip the tips off the primary flight feather.

Steve Salisbury :

Dann :

23 Apr 2012 12:28:12pm

Asymmetrical primaries are certainly more efficient (which is why they are prevalent in extant volant theropods), however symmetrical primaries are still not proof of a lack of active flight in ancestral avians.

Symmetrical primaries however would have needed to be more robust to withstand the extra torsional forces, making them heavier than modern asymmetrical equivalents. However we shouldn't expect the first non-avian theropods that experimented with active flight (as opposed to gliding or parachuting) to have fully-modern asymmetrical primaries.